The invention is based on a priority application EP 04 291 978.7 which is hereby incorporated by reference.
The present invention relates to a method for improving access network selection in the context of discontinuous coverage access networks.
Discontinuous coverage access networks are radio access networks which do not provide a continuous radio coverage contrary to conventional second or third generation radio access networks as GSM or UMTS. Such discontinuous coverage access networks are constituted by islands of coverage supporting very high bit rates and low power cells. Such networks are commonly referred to as fourth generation access networks. They are best adapted to provide video/audio streaming services and fast download or upload of large data volumes.
The islands of radio coverage are nevertheless separated by zones of non-radio coverage so that usual hand over between cells is not to be realized by common techniques.
Moreover, if several radio access networks are co-existing in a same area, an advantageous feature is to select the best appropriate radio access network for providing a service requested by a customer while taking into account for example the capabilities of the different access networks, their availability and customer respective operator wishes.
The easiest method for such an access network selection would be to provide a central control/switch element above all possible access networks and which triggers the selection or the change of access network.
Nevertheless, in the context of discontinuous coverage access networks or in the context of co-existence of continuous and discontinuous coverage access networks such a central control/switch element should be able to cope with caching techniques mandatory in discontinuous coverage radio access networks. Indeed, caches at the different levels of the discontinuous coverage access network architecture may be filled with data during the time when the terminal is in a non coverage area. These cached data should be delivered with delay after the terminal has entered a new zone of radio coverage. If at this moment another access network is selected for the customer all cached data may be lost, if no appropriate measure is taken, rendering a simple access network selection incompatible with a seamless service.
A known solution would be that the content server retransmits these data if lost data are detected at the terminal. An appropriate retransmission protocol for example TCP would then take care for the missing data retransmission. However, such retransmissions generate a long latency delay where for example TCP is not adapted to a long latency delay and necessitate an important overhead. This is not adapted to streaming services which cannot cope with long retransmissions due to the high throughput of data to deliver. Moreover, retransmission protocols as the TCP protocols are not fitted for heterogeneous networks mixing fixed or wireless links.
A particular object of the present invention is to provide a method for providing access network selection in the context of discontinuous coverage access networks.
Another object of the invention is to provide an entity of the radio access network supporting the method.